A metal workpiece ultrafast laser processing method based on surface quality feedback

Abstract

The application belongs to the technical field of metal workpiece surface finishing related to additive manufacturing equipment and laser rapid forming device, and particularly relates to a metal workpiece ultrafast laser processing method based on surface quality feedback, which comprises the following steps: pretreating a surface to be processed, measuring an initial maximum height difference and an initial arithmetic average roughness, identifying a surface working condition according to the initial maximum height difference and the initial arithmetic average roughness, matching a laser removal strategy, determining a metal material single-pulse ablation threshold, determining a laser average output power in combination with an acting spot size at a defocusing position and a processing spot diameter, cooperatively controlling a pulse overlap rate and a scanning line overlap rate according to the processing spot diameter, a repetition frequency, a scanning speed and a scanning line spacing, processing by adopting an X, Y direction alternating vertical cross scanning mode, and dynamically adjusting a scanning round and determining a termination condition according to a cumulative removal depth and roughness change. The application realizes closed-loop regulation and control of an additive manufacturing metal workpiece ultrafast laser processing process, and improves surface quality, consistency and processing yield.

Description

Technical Field

[0001] This application belongs to the field of surface finishing technology for metal workpieces related to additive manufacturing equipment and laser rapid prototyping equipment. Specifically, it relates to an ultrafast laser processing method for metal workpieces based on surface quality feedback. Background Technology

[0002] Additive manufacturing equipment and laser rapid prototyping equipment are widely used in the rapid fabrication of metal components, the forming of complex structures, and the manufacturing of high-performance parts. During the manufacturing, debugging, and application of this equipment, the surface quality of the metal workpiece directly affects the forming accuracy, component fit accuracy, assembly reliability, and service performance. For metal workpieces obtained through laser rapid prototyping, the surface often has undulations, attached particles, microscopic irregularities, or local height differences, requiring subsequent leveling, finishing, or polishing processes to improve surface quality.

[0003] Ultrafast lasers, such as femtosecond and picosecond lasers, feature short pulse widths, high peak power, and small heat-affected zones, enabling high-precision micro-removal of material surfaces under relatively low heat-affected conditions. Compared to mechanical and chemical polishing, ultrafast laser surface treatment offers advantages such as non-contact operation, high precision, selective local processing, and ease of automation integration, making it suitable for surface finishing of additive manufacturing equipment, laser rapid prototyping equipment, and related metal workpieces.

[0004] Existing laser surface treatment technologies typically use a laser beam to act on the workpiece surface, removing surface material through mechanisms such as melting, vaporization, or ablation to reduce surface roughness or improve surface smoothness. For example, existing technologies include schemes for polishing metal surfaces using laser remelting and surface tension leveling effects, schemes that measure surface morphology and perform layered leveling of protruding areas before polishing, and schemes that achieve surface finishing of metal workpieces through composite processing of lasers with different pulse widths.

[0005] However, the above technologies still have shortcomings when applied to additive manufacturing equipment, laser rapid prototyping equipment, and related metal workpiece surface finishing: 1. They mostly use preset parameters for processing, lacking the ability to dynamically adjust parameters according to changes in surface quality during processing, making it difficult to adapt to different initial surface states; 2. The control of laser energy density is not precise enough, and the matching relationship between defocusing amount, spot size, and material ablation threshold is not fully considered, which can easily lead to under-processing or over-processing; 3. The scanning strategy is relatively simple, which can easily form periodic textures on the processed surface, and lacks coordinated control of spot overlap rate and line overlap rate; 4. The surface state parameters such as initial maximum height difference and initial arithmetic mean roughness are not fully utilized for processing strategy selection, making it difficult to balance processing efficiency and surface quality.

[0006] Therefore, there is an urgent need to provide an ultrafast laser processing method suitable for additive manufacturing equipment, laser rapid prototyping equipment, and related metal workpiece surface finishing, which can match the processing strategy according to the workpiece surface condition, and improve the consistency, uniformity and stability of surface processing through closed-loop feedback, precise laser energy regulation and collaborative scanning control. Summary of the Invention

[0007] To address the shortcomings of existing technologies, such as lack of adaptability in open-loop control, coarse energy density control, surface texture deterioration due to a single scanning strategy, and failure to match processing strategies based on initial state, this application provides an ultrafast laser processing method for metal workpieces based on surface quality feedback. By introducing a real-time surface roughness monitoring and dynamic adjustment mechanism for processing cycles, combined with spot size calculation based on defocusing amount and precise laser energy density matching strategy, and constructing a coupling relationship between spot overlap rate and line overlap rate and a vertical cross-scanning method, this method intelligently matches the removal allowance and iteration step size based on the initial surface state of the workpiece. This achieves closed-loop adaptive control of the processing process, stable precision processing under non-thermal ablation window, homogenization removal of surface texture, and differentiated and efficient processing of workpieces with different initial states. As a result, it improves the yield, consistency, surface integrity, surface uniformity, and process applicability of metal workpiece processing.

[0008] This application provides an ultrafast laser processing method for metal workpieces based on surface quality feedback, the method comprising:

[0009] Step 1: Pre-treat the surface of the metal workpiece, measure the initial maximum height difference and initial arithmetic mean roughness of the surface to be processed, and identify the working condition based on the initial maximum height difference to determine the laser removal strategy;

[0010] Step 2: Determine the single-pulse ablation threshold of the metal material, calculate the size of the active spot and the diameter of the processing spot at the defocus position, and determine the average output power of the laser by combining the single-pulse ablation threshold, the laser repetition frequency and the active spot size;

[0011] Step 3: Determine the pulse overlap rate and scan line overlap rate based on the processing spot diameter, laser repetition frequency, galvanometer scanning speed, and scan line spacing. Under the condition that the pulse overlap rate and scan line overlap rate are equal, use an alternating vertical cross-scanning method in the X and Y directions to process the surface to be processed.

[0012] Step 4: Set the target cumulative removal depth based on the initial maximum height difference. Determine the theoretical total number of scans based on the removal depth of a single vertical cross scan. Determine the number of scans per round of processing based on the working condition type corresponding to the initial maximum height difference. After the nth round of processing, obtain the current cumulative removal depth and the current arithmetic mean roughness. Compare the current arithmetic mean roughness with the reference roughness of the (n-1)th round, and compare the current cumulative removal depth with the target cumulative removal depth. When the current arithmetic mean roughness > the reference roughness and the current cumulative removal depth > the target cumulative removal depth, update the degradation counter. When the current arithmetic mean roughness ≤ the reference roughness, reset the degradation counter and update the historical best roughness and the reference roughness. Determine whether to stop processing or enter the next iteration based on the degradation counter result and / or the roughness convergence result.

[0013] In the preferred implementation, further,

[0014] Step 4 includes:

[0015] Step 4.1: Set the target cumulative removal depth based on the initial maximum height difference, so that the target cumulative removal depth has a safety margin on the basis of covering the initial maximum height difference, and the target cumulative removal depth is 1.5 to 2.0 times the initial maximum height difference;

[0016] Target cumulative removal depth for:

[0017]

[0018] In the formula: This refers to the initial maximum height difference measured in step 1; For safety factors, the value ranges from 1.5 to 2.0;

[0019] Step 4.2: Based on the removal depth of a single vertical cross-scan Cumulative removal depth with target Calculate the number of basic scan groups The number of scans per processing cycle is dynamically configured based on the large-scale removal or fine homogenization conditions characterized by the initial maximum height difference. ;

[0020] Step 4.3: First, initialize the first round of planned scan count, surface roughness baseline value, degradation counter, historical best roughness, and convergence threshold, then... After the wheel machining is completed, the current cumulative removal depth and the current arithmetic mean roughness are obtained. Based on the change of the current arithmetic mean roughness relative to the previous round reference roughness, and the achievement of the current cumulative removal depth relative to the target cumulative removal depth, the degradation counter, historical best roughness and reference roughness are updated to establish an iterative execution and feedback control process.

[0021] Step 4.4: Determine the termination condition based on the deterioration counter and the relative change rate of surface roughness. When quality deterioration occurs in two consecutive rounds and the current cumulative removal depth reaches or approaches the target cumulative removal depth, or when the relative change rate of surface roughness is less than the preset convergence threshold and the current cumulative removal depth reaches or approaches the target cumulative removal depth, or when the relative change rate of surface roughness in two consecutive rounds is less than the convergence threshold, terminate the processing and retain the historical best roughness state as the final result. Otherwise, increase the cumulative planned scan count and enter the next iteration.

[0022] In the preferred implementation, further, in step 4.2, the number of basic scan groups... for:

[0023]

[0024] In the formula: The cumulative removal depth of the target; d is the removal depth of a single vertical cross-scan. It is a rounding function;

[0025] Number of scans per round according to The surface to be processed is divided into "large allowance removal condition" or "fine homogenization condition". When step 1 identifies the surface to be processed as being in the large allowance removal condition, Set to a larger value; when step 1 identifies the surface to be processed as being in a fine homogenization condition, Set to a smaller value.

[0026] In the preferred implementation, further, in step 4.3, before formally entering the first round of processing, the state initialization for round 0 is performed first, and the number of planned scans for the first round is set. The initial arithmetic mean roughness measured in step 1 is... Set as the reference value for surface roughness in the previous round and initialize the degradation counter. Historical best roughness and convergence threshold The convergence threshold The value range is 3%-5%;

[0027] In the Obtain the current cumulative removal depth after the wheel processing is completed. and the current arithmetic mean roughness and will Compared with the previous reference roughness as well as Cumulative removal depth with target Perform joint comparison; when and or At that time, update the deterioration counter to ;when and At the same time, the degradation counter remains unchanged, and the reference roughness is... Keep unchanged or press Update; when At that time, the deterioration counter will be reset to zero, and in Update historical best roughness At the same time Updated to .

[0028] In the preferred implementation, further, in step 4.4, based on the deterioration counter... To determine the protection against persistent degradation, when And the current cumulative removal depth meets the requirements. or If the processing is determined to have entered a stage of continuous quality degradation, processing should be terminated immediately, and the historical best surface roughness should be retained. The corresponding state is taken as the final result.

[0029] In a preferred implementation, further, in step 4.4, the relative change rate of surface roughness... Calculate using the following formula:

[0030]

[0031] In the formula: The surface roughness reference value from the previous round before entering this round of judgment; The current arithmetic mean roughness obtained in this round of testing; the convergence threshold. The value range is 3%-5%; when and When the processing reaches a convergence state, the processing is terminated; or when two consecutive rounds satisfy the condition... If the above termination conditions are not met, the cumulative planned scan count is updated. Then, it will proceed to the next round of iterative processing.

[0032] In a preferred implementation, further, in step 3, the pulse overlap rate... Scan line overlap rate ,when At that time, we can obtain:

[0033]

[0034] In the formula: v is the laser repetition frequency; v is the galvanometer scanning speed. The diameter of the processing spot; L is the line spacing between two adjacent scan lines.

[0035] In a preferred implementation, further, in step 3, the vertical cross-scanning strategy specifically includes: setting the area to be processed as a processing path containing at least two scanning levels, wherein the scanning direction of the i-th scanning path is perpendicular to the scanning direction of the (i+1)-th scanning path; within each scanning level, the scanning speed v of the galvanometer system and the repetition frequency of the laser are controlled collaboratively. This results in a higher overlap rate between adjacent pulse spots along the scanning direction. Satisfy: 50% ≤ ≤98%; simultaneously, the line spacing L between adjacent scan trajectories is set to ensure that the overlap rate of scan lines perpendicular to the scanning direction is ≤98%; Satisfy: 50% ≤ ≤98%; where the spot overlap rate overlap with scan line They are configured to be equal, or the absolute value of the difference between the two is ≤10%, in order to achieve isotropic energy deposition on the workpiece surface and uniform distribution of removal amount.

[0036] In a preferred implementation, the laser removal strategy in step 1 further includes a rapid peak-shaving mode for surfaces with large margins and a fine homogenization mode for surfaces with small margins. The rapid peak-shaving mode is used when the initial maximum height difference is greater than a preset threshold, and the fine homogenization mode is used when the initial maximum height difference is less than or equal to the preset threshold.

[0037] In a preferred implementation, further, in step 2, the laser energy density is slightly higher than the material ablation threshold, and the average output power of the laser is controlled to ensure that the single-pulse laser energy density on the defocused surface is... Satisfying the relation:

[0038]

[0039] In the formula: The single-pulse ablation threshold of the material; For safety, the preferred value range is 1.05-1.35;

[0040] laser average output power for:

[0041]

[0042] In the formula: For safety factor; The single-pulse ablation threshold of the material; The repetition frequency of the laser; Defocus amount The actual effective spot radius at the location; This is the defocusing amount.

[0043] The beneficial effects of this application are:

[0044] 1. This application measures the initial maximum height difference and initial arithmetic mean roughness of the surface to be processed before processing, and uses the initial maximum height difference as the basis for distinguishing processing conditions, so that the laser removal strategy corresponds to the degree of undulation of the workpiece surface. For surfaces with large initial undulations, processing can be arranged with a larger removal allowance, and for surfaces with small initial undulations, processing can be carried out with a smaller single-round removal amount. This reduces the insufficient removal, local overcutting or wasted processing time caused by using the same processing method for different initial surface conditions, and makes the selection of processing parameters have a clear basis for surface quality.

[0045] 2. In determining the average output power of the laser, this application first measures the single-pulse ablation threshold of the metal material, then calculates the size of the active spot and the diameter of the processed spot at the defocus position, and determines the power parameters in combination with the laser repetition frequency. This processing method incorporates the material ablation conditions, defocus state and actual spot size into the same power calculation process, reduces the energy deviation per unit area caused by defocus, keeps the material removal within a more stable ablation range, reduces the risk of recast residue, microcracks, local overheating and heat-affected zone expansion, and helps maintain the integrity of the processed surface.

[0046] 3. This application determines the pulse overlap rate and scan line overlap rate based on the processing spot diameter, laser repetition frequency, galvanometer scanning speed and scan line spacing, and controls the two to be equal before scanning processing. After the coverage of adjacent pulses in the scanning direction is consistent with the coverage between adjacent scan lines, the energy distribution in the unit area is closer to a uniform state, which can reduce the striped texture, local residue and uneven removal depth caused by scanning in a single direction.

[0047] 4. This application uses an alternating vertical cross-scanning method in the X and Y directions to process the surface to be processed. This weakens the directional removal differences formed by the scanning in the previous direction in the scanning in the next direction. Compared with unidirectional reciprocating scanning, this method can make the material removal more evenly distributed in two orthogonal directions, reduce the possibility of continuous accumulation of processing texture along a single direction, and help improve the flatness of the processed surface and the roughness difference between regions.

[0048] 5. This application sets the target cumulative removal depth based on the initial maximum height difference, and determines the theoretical total number of scans based on the removal depth of a single vertical cross scan. At the same time, it determines the number of scans per processing round according to the working condition type. The total removal depth is used to limit the final amount of material removed, and the number of scans per round is used to control the processing range of a single iteration. This setting can retain the necessary removal capacity on surfaces with large undulations, and can also reduce the possibility of over-processing on surfaces with small undulations, so that the removal amount control is adapted to the initial state of the surface.

[0049] 6. After the nth round of processing, this application obtains the current cumulative removal depth and the current arithmetic mean roughness, and compares the current arithmetic mean roughness with the reference roughness of the n-1th round. At the same time, it compares the current cumulative removal depth with the target cumulative removal depth. When the current arithmetic mean roughness is greater than the reference roughness and the current cumulative removal depth is greater than the target cumulative removal depth, the roughness deterioration is recorded. When the current arithmetic mean roughness is not greater than the reference roughness, the deterioration record is cleared and the historical best roughness and reference roughness are updated. Thus, whether processing continues no longer depends solely on the preset number of scans, but also on the changes in surface roughness and the material removal depth. This can reduce the situation where scanning continues after the surface quality has deteriorated or is close to the target removal amount.

[0050] 7. This application determines whether to stop processing or proceed to the next iteration based on the deterioration count results and roughness convergence results. When the roughness does not continue to improve after continuous processing, or when the roughness continues to deteriorate after reaching the target removal depth, subsequent scanning can be stopped. When the roughness still shows an improvement trend and the stopping condition has not yet been met, the next round of processing can be started. This judgment method can reduce invalid scanning and excessive removal, reduce the risk of workpiece scrap, and make different batches of workpieces have a more similar surface quality state when processing is terminated. Attached Figure Description

[0051] Figure 1 This is a flowchart of the ultrafast laser processing method for metal workpieces based on surface quality feedback according to the present invention;

[0052] Figure 2 This is a schematic diagram of the laser processing equipment used in the ultrafast laser processing method for metal workpieces based on surface quality feedback according to the present invention.

[0053] Figure 3 This is a surface morphology image of an unprocessed workpiece in an embodiment of the ultrafast laser processing method for metal workpieces based on surface quality feedback of the present invention.

[0054] Figure 4 This is an example of the surface morphology of a workpiece obtained after finishing in an embodiment of the ultrafast laser processing method for metal workpieces based on surface quality feedback of the present invention.

[0055] Figure 5 This is a comparison image of the surface morphology of the workpiece after finishing and the original morphology in an embodiment of the ultrafast laser processing method for metal workpieces based on surface quality feedback of the present invention. Detailed Implementation

[0056] To enable those skilled in the art to better understand the technical solutions of this application, the following will provide a more detailed description of this application in conjunction with the accompanying drawings and embodiments.

[0057] The directional terms such as above, below, left, right, front, and back used in this application are based on the positional relationships shown in the attached drawings. Different attached drawings may result in different positional relationships, therefore they should not be interpreted as limitations on the scope of protection.

[0058] In this application, the terms "installation," "connection," "interlocking," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, an integral connection, a mechanical connection, an electrical connection, or a connection that allows communication between components. They can also refer to a direct connection or an indirect connection through an intermediate medium. They can refer to the internal connection of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0059] This invention describes an ultrafast laser processing method for metal workpieces based on surface quality feedback. It aims to solve the problem that it is difficult to balance removal efficiency, surface flattening effect and processing termination control in the existing surface finishing process of metal workpieces. By establishing a working condition identification mechanism based on the initial maximum height difference, and combining it with defocus spot parameter calculation, vertical cross-scanning strategy with overlap rate matching, and dynamic iterative control driven by roughness feedback, stable, uniform and low thermal impact finishing of metal workpiece surfaces can be achieved.

[0060] As per the instruction manual Figure 1 This invention discloses an ultrafast laser processing method for metal workpieces based on surface quality feedback, applicable to the field of ultrafast laser surface processing of metal materials, particularly for reducing surface roughness, smoothing peaks and valleys, and improving surface quality of additively manufactured metal workpieces such as those produced by SLM. The method includes:

[0061] Step 1: Pre-treat the surface of the metal workpiece, measure the initial maximum height difference and initial arithmetic mean roughness of the surface to be processed, and identify the working condition based on the initial maximum height difference to determine the laser removal strategy.

[0062] As per the instruction manual Figure 2The metal workpiece to be processed is clamped in the laser processing system. The laser processing system mainly consists of an ultrafast laser optical path unit, a three-dimensional motion platform, a surface pretreatment unit, an initial morphology measurement unit, and a main control computer 10. The ultrafast laser optical path unit includes an ultrafast laser 1, a beam expander 2, a high-reflectivity mirror 3, a high-reflectivity mirror 4, a high-speed galvanometer scanning head 5, and a large-aperture flat-field focusing mirror 6. The pulsed laser beam output from the laser is transmitted sequentially through the beam expander 2, the high-reflectivity mirror 3, the high-reflectivity mirror 4, the high-speed galvanometer scanning head 5, and the large-aperture flat-field focusing mirror 6, and then acts on the surface of the metal workpiece 11 fixed in the fixture 7. The three-dimensional motion platform integrates a precision linear displacement module 8 orthogonally distributed along the X-axis, Y-axis, and Z-axis, and a special fixture 7 fixed to the precision linear displacement module 8, used to achieve precise positioning of the metal workpiece 11 in space and switching of processing areas. The main control computer 10 is electrically connected to the ultrafast laser 1, the galvanometer scanning head 5, the precision linear displacement module 8, and the initial morphology measurement unit, respectively, and is used to collect measurement data and control subsequent processing parameters.

[0063] The surface pretreatment unit preferably includes an ultrasonic cleaner, a cleaning fluid container, and a drying device, used to clean and dry the surface of the metal workpiece 11 before the initial morphology measurement. The initial morphology measurement unit preferably employs a three-dimensional surface profilometer 9. The three-dimensional surface profilometer 9 can be a white light interferometric surface profilometer, a laser confocal surface profilometer, or a surface roughness measuring instrument with three-dimensional surface morphology acquisition capabilities. It is used to collect the height data of each sampling point within the measurement area of ​​the surface to be processed relative to a reference datum surface, and to calculate the initial maximum height difference of the surface to be processed. and initial arithmetic mean roughness .

[0064] In step 1, the metal workpiece 11 is first pretreated using a surface pretreatment unit. Specifically, the workpiece 11 is placed in an ultrasonic cleaner and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water to remove oil, powder residue, cutting fluid residue, oxide deposits, and other loose contaminants from the workpiece surface. Preferably, the ultrasonic cleaning time for each cleaning solution is 3-10 minutes. After cleaning, the workpiece 11 is dried using clean compressed air, nitrogen, or constant-temperature hot air to keep the workpiece surface clean and dry.

[0065] After preprocessing, the metal workpiece 11 is fixed on the fixture 7, and the surface to be processed is moved to the initial shape measurement position by the precision linear displacement module 8. The three-dimensional surface profilometer 9 performs surface scanning on the measurement area A of the surface to be processed to obtain the height data of each sampling point in the measurement area relative to the reference average surface.

[0066] In this embodiment, the initial maximum height difference of the surface to be processed This refers to the vertical height difference between the highest peak and the lowest valley point among all sampling points within the same measurement area A. Specifically, let the height of each sampling point within the measurement area relative to the reference average surface be denoted as . The height of the highest peak within the measurement area is:

[0067] (1)

[0068] The lowest valley floor height within the measurement area is:

[0069] (2)

[0070] Then the initial maximum height difference of the measurement area for:

[0071] (3)

[0072] It reflects the total undulation range from the most prominent peak to the deepest valley within the measurement area. It directly characterizes the peak-valley difference on the surface to be processed, making it suitable as a core basis for subsequent material removal depth setting and working condition identification. For discrete measurement data output by the profilometer, if a total of [data missing] samples are collected within the measurement area... There are N sampling points, where M represents the number of sampling points in one direction of the measurement area, such as the number of sampling points in the X direction, and N represents the number of sampling points in another direction of the measurement area, such as the number of sampling points in the Y direction. The height of each sampling point is ,but It can also be calculated in the following discrete form:

[0073] (4)

[0074] In this embodiment, the initial arithmetic mean roughness This refers to the average area of ​​the absolute height of each sampling point relative to the reference average surface within the measurement area. This parameter reflects the average amplitude of the microscopic undulations of the entire measurement area surface and is used to characterize the overall surface roughness. Its continuous form is:

[0075] (5)

[0076] In the formula: A is the area of ​​the measurement region; The height of the measurement point relative to the reference average surface; This is the absolute value of the height deviation at that point. For the discrete sampling data output by the 3D surface profilometer 9, if there are a total of [missing information] within the measurement area... There are 1 sampling point, and the height value of each sampling point is 1. ,but It can be calculated in the following discrete form:

[0077] (6)

[0078] In the formula: Characterizes the initial maximum height difference within the measurement area; It characterizes the overall average roughness of the surface. Combining the two allows for a more complete characterization of the initial state of the surface to be processed.

[0079] The 3D surface profilometer 9 will measure and Send to computer 10, computer 10 records As the core benchmark for setting the removal amount in subsequent processing, and based on Perform working condition identification to determine the corresponding laser removal strategy.

[0080] Specifically, a threshold for identifying operating conditions can be set. ,when When the current surface to be processed is determined to be in a condition of large-scale material removal; when At that time, it is determined that the surface to be processed is in a fine and homogeneous state. For typical laser additive manufacturing of metal parts, it can be taken as follows: As a statistical reference threshold. At this time, when... When, usually corresponding This indicates a large peak-to-valley difference on the surface, with numerous sharp peaks and deep valleys. The system identifies this as a large-scale removal condition, and subsequent laser removal strategies focus on improving single-round removal efficiency and rapid peak reduction. When, usually corresponding This indicates that the surface is in a state of low peak-to-valley difference, which the system identifies as a fine homogenization process. Subsequent processing strategies focus on suppressing overcutting and improving surface convergence and uniformity. It should be noted that the 80μm and 8μm values ​​mentioned above are only typical process statistical reference values ​​and do not constitute a limitation on the scope of protection of this application. For metal workpieces from different material systems or different forming processes, the threshold values ​​may vary. Adjustments can be made based on preliminary experimental results, database statistics, or production experience.

[0081] After step 1, the system should output at least the following parameters or judgment results for subsequent steps: initial maximum height difference. Initial arithmetic mean roughness The system includes the working condition identification results and the corresponding initial laser removal strategy labels. The initial laser removal strategy labels include at least two categories: "large margin removal working condition" and "fine homogenization working condition," which are used to guide the setting of target cumulative removal depth, number of scans per round, power settings, and termination logic in subsequent steps.

[0082] Step 2: Determine the single-pulse ablation threshold of the metal material, calculate the size of the active spot and the diameter of the processing spot at the defocus position, and determine the average output power of the laser by combining the single-pulse ablation threshold, the laser repetition frequency and the active spot size.

[0083] Step 2 is still completed collaboratively by the main control computer 10, the ultrafast laser 1, the beam expander 2, the high-reflectivity mirror 3, the high-reflectivity mirror 4, the high-speed galvanometer scanning head 5, the large-aperture flat-field focusing mirror 6, the precision linear displacement module 8, and the fixture 7. The main control computer 10 is used to set the wavelength, pulse width, single pulse energy, repetition frequency, and average power of the ultrafast laser 1, and adjusts the spatial position of the workpiece 11 surface relative to the focal plane of the flat-field focusing mirror 6 through the precision linear displacement module 8 in the Z-axis direction, so that the processing plane deviates from the focal plane by a predetermined distance along the direction perpendicular to the normal of the worktable. The Z-axis direction is perpendicular to the normal direction of the horizontal worktable. Preferably, the laser beam is incident on the workpiece surface in a normal direction, i.e., the incident angle is approximately... .

[0084] In this embodiment, the single-pulse ablation threshold , refers to the minimum single-pulse energy density at which a material surface just begins to undergo stable ablation under given laser wavelength, pulse width, and incident conditions. The unit is usually 100 kJ / m². or In other words, when the peak energy density of a single-pulse laser on a material surface is below this threshold, effective removal typically does not occur; when the peak energy density reaches or slightly exceeds this threshold, repeatable micro-ablation begins on the material surface. Therefore, These are the basic parameters for setting the average output power and controlling the actual removal status.

[0085] In one embodiment, the single-pulse ablation threshold The threshold ablation test can be used for determination. Specifically, a sample with the same material or similar surface condition as the metal workpiece 11 to be processed is selected as the threshold test sample. This sample is fixed on the fixture 7, and the ultrafast laser 1 is controlled by the main control computer 10 to operate in single-pulse output mode. Alternatively, under the condition that the positions of adjacent pulses do not overlap, several ablation points are formed on the sample surface using a single-point single-pulse method. During the experiment, the single-pulse energy is gradually changed. The diameter of each ablation point was measured using an optical microscope, a three-dimensional surface profilometer, or other microscopic measuring devices.

[0086] Preferably, the Gaussian beam single-pulse ablation threshold fitting method can be used for determination. For a single-pulse laser beam with an approximately Gaussian distribution, its energy density distribution on the material surface satisfies Gaussian distribution characteristics. Let the beam radius at the focal plane be... When the energy of a single pulse is At that time, the peak energy density at the center of the Gaussian beam satisfy:

[0087] (7)

[0088] When a single pulse is applied to the material surface to form an ablation spot, the square of the ablation spot diameter... The natural logarithm of the single pulse energy They approximately satisfy a linear relationship:

[0089] (8)

[0090] In the formula: The diameter of the ablation spot; The threshold pulse energy is obtained by linearly fitting the squared ablation spot diameter measured at different single pulse energies. and focal plane beam radius Furthermore, the single-pulse ablation threshold It can be calculated using the following formula:

[0091] (9)

[0092] The above method can quantify the critical state at which ablation just occurs in a material into a single-pulse ablation threshold. This provides a basis for setting the power under subsequent defocused spot conditions.

[0093] It should be noted that the single-pulse ablation threshold It is not a fixed material constant, but rather depends on the laser wavelength, pulse width, polarization state, surface condition, and environmental conditions. Therefore, it is preferable to measure it under laser pulse width, wavelength, incident mode, and environmental conditions that are the same as or substantially consistent with the actual processing. This is to improve the accuracy and feasibility of subsequent power settings.

[0094] Obtaining the single-pulse ablation threshold Then, according to the preset process defocusing amount Calculate the size of the effective light spot at the defocus position. Wherein, the defocus amount... , refers to the axial offset distance of the workpiece surface to be processed along the Z-axis relative to the theoretical focal plane of the flat-field focusing lens 6. When the workpiece surface is below the focal plane, it can be recorded as positive defocus, indicating that the processed surface deviates from the position of the minimum focused spot. By setting an appropriate defocus amount, the spot diameter can be increased, the energy density per unit area can be reduced, and the spatial distribution can be more uniform, thereby avoiding deep pits and local heat accumulation caused by excessive energy concentration at the focal point.

[0095] In this embodiment, it is assumed that the laser beam output by the ultrafast laser 1 approximately follows the Gaussian beam propagation law. Let the beam waist radius at the focal plane be... The laser wavelength is Rayleigh length for:

[0096] (10)

[0097] In this application, the effective spot size is the laser spot radius on the workpiece surface at the defocus position. When the workpiece surface has a defocusing amount relative to the focal plane At that time, the radius of the light spot at the defocus position satisfy:

[0098] (11)

[0099] Will Substitute into the formula ,available:

[0100] (12)

[0101] Therefore, the diameter of the processing spot at the defocus position for:

[0102] (13)

[0103] In the formula: This indicates the radius of the laser spot on the workpiece surface at the defocused position; This indicates the effective spot diameter of a single pulse on the workpiece surface during processing.

[0104] In one embodiment, defocus amount The setting can be based on the laser's maximum average power, the material's single-pulse ablation threshold, and the target processing uniformity, with a preferred value range of 0.1mm-6.0mm. Generally speaking, the defocusing amount... The increase will lead to an increase in the spot diameter Increasing the energy density reduces the peak energy density at a single point, broadens the non-thermal ablation process window, and improves the consistency of surface removal; however, if If the defocusing amount is too large, the energy density may drop below the threshold, thereby weakening the effective removal capability. Therefore, the defocusing amount is preferably proportional to the maximum average power of the laser and inversely proportional to the material ablation threshold, and should be selected comprehensively based on the specific material and equipment capabilities.

[0105] After obtaining the single-pulse ablation threshold Laser repetition frequency and the radius of the light spot at the defocus position Then, the average output power of the laser was further determined. The basic principle is to make the peak energy density of the single pulse slightly higher than the single pulse ablation threshold of the material at the defocus position, so as to ensure stable ablation while avoiding significant thermal effects and deep ablation pits due to excessive energy.

[0106] For a single-pulse laser beam with an approximately Gaussian distribution, if the single-pulse energy is... The peak energy density at the defocus position is:

[0107] (14)

[0108] To ensure that the actual processing is carried out in a stable removal state slightly above the ablation threshold, a single-pulse energy density safety factor is introduced. ,make:

[0109] (15)

[0110] In the formula: For safety, a value in the range of 1.05-1.35 is preferred. This safety factor ensures that the peak energy density at the defocus position is higher than the single-pulse ablation threshold, while avoiding a value far exceeding the threshold that would exacerbate the thermal effect.

[0111] Combining the relationships in formulas (14) and (15) above, we can obtain the single pulse energy. for:

[0112] (16)

[0113] Furthermore, due to the average output power of the laser With single pulse energy and repetition frequency The following conditions must be met:

[0114] (17)

[0115] Therefore, the average output power of the laser It can be represented as:

[0116] (18)

[0117] Furthermore, if the processing spot diameter is considered... If we express that, then the above formula can also be written as:

[0118] (19)

[0119] The computer 10 calculates the target average output power according to the formula. The energy density is then sent to ultrafast laser 1 for parameter setting. Through these settings, the central peak energy density at the defocus position can be maintained at a level slightly above the material's single-pulse ablation threshold, thereby triggering stable and uniform non-thermal ablation under single-pulse action; simultaneously, since the workpiece surface is located below the focal plane... The processing spot is larger than the focal spot, and the energy density distribution is more gradual. This helps to avoid local over-ablation, deep pit effect and heat accumulation caused by excessive energy at the focal point, thereby achieving uniform material removal and surface flattening of the metal surface.

[0120] After step 2, the system outputs the following parameters: current material and single-pulse ablation threshold under the current pulse width condition. Preset defocus amount The radius of the light spot at the out-of-focus position. Processing spot diameter The corresponding average output power of the laser The above output parameters are used to construct the pulse overlap rate, scan line overlap rate, and scanning strategy in step 3, and for the processing removal amount and surface quality feedback control in step 4.

[0121] Step 3: Determine the pulse overlap rate and scan line overlap rate based on the processing spot diameter, laser repetition frequency, galvanometer scanning speed, and scan line spacing. Under the condition that the pulse overlap rate and scan line overlap rate are equal, use an alternating vertical cross-scanning method in the X and Y directions to process the surface to be processed.

[0122] Step 3 is completed collaboratively by the main control computer 10, the ultrafast laser 1, the high-speed galvanometer scanning head 5, the large-aperture flat-field focusing lens 6, and the precision linear displacement module 8. The main control computer 10 sends scanning trajectory signals to the high-speed galvanometer scanning head 5 to control the laser focus to perform high-speed reciprocating scanning along a preset direction on the surface of the workpiece 11. Simultaneously, the main control computer 10 also controls the precision linear displacement module 8 to switch the position of the workpiece 11 within a macroscopic range and perform area stitching, ensuring continuous implementation of multiple scanning layers on a large-area surface to be processed. In actual processing, the galvanometer scanning head 5 is mainly responsible for high-speed linear scanning of micro-areas, while the precision linear displacement module 8 is mainly responsible for macroscopic movement and stitching coverage of the processing area.

[0123] In this embodiment, the pulse overlap rate This refers to the degree of overlap along the scanning direction of adjacent working spots formed by two consecutive laser pulses on the workpiece surface within the same scanning line. This parameter characterizes the connection and coverage between adjacent pulse pits along the scanning direction and is one of the important parameters for controlling the uniformity of surface removal. Let the diameter of the processing spot calculated in step 2 be... The laser repetition frequency is The galvanometer scanning speed is The center-to-center distance between two adjacent pulses in the scanning direction is... for:

[0124] (20)

[0125] In the formula: The unit is mm / s; The unit can be Hz; This represents the distance the laser focus moves along the scanning direction within one pulse cycle. Therefore, the pulse overlap rate... for:

[0126] (twenty one)

[0127] Will Substituting into formula (21), we get:

[0128] (twenty two)

[0129] Therefore, the pulse overlap rate With scan speed Inversely proportional to the repetition frequency of the laser and processing spot diameter The overlap is directly proportional to the scanning speed. When the scanning speed decreases, the repetition frequency increases, or the spot diameter increases, the overlap between adjacent pulses increases; conversely, the overlap decreases.

[0130] In a preferred embodiment, the pulse overlap rate The ablation rate should be controlled within the range of 50%-98% to ensure seamless connection between ablation pits formed by individual pulses and avoid unprocessed gaps in the scanning direction due to excessively sparse pulses. Preferably, when the surface to be processed is in a relatively fine homogenization stage, the ablation rate can be appropriately increased. To enhance the continuity of surface removal; when the surface to be processed is in the stage of large-scale removal, the removal capacity can be appropriately reduced while ensuring continuous coverage. In order to balance removal efficiency.

[0131] In this embodiment, the scan line overlap rate This refers to the degree of overlap between adjacent working areas of two adjacent scan lines perpendicular to the scanning direction. This parameter characterizes the lateral coverage between scan lines and is an important factor affecting the uniformity of energy distribution and surface texture formation across the entire area. Let the line spacing between two adjacent scan lines be... The diameter of the processing spot is Then the scan line overlap rate for:

[0132]

[0133] In the formula: This represents the distance between the centers of adjacent scan lines perpendicular to the scanning direction. When The smaller the value, the greater the lateral overlap of the scan lines; when As the overlap increases, the lateral overlap decreases. To avoid strip-like unprocessed areas between scan lines, it is preferable to maximize the scan line overlap rate. Maintaining overlap with pulse Similar levels.

[0134] In this embodiment, to ensure that the energy input distribution on the surface to be processed is as consistent as possible in the scanning direction and the vertical scanning direction, it is preferable to control the pulse overlap rate. overlap with scan line They are equal or approximately equal, that is, they satisfy the condition that they are equal or approximately equal. .

[0135] Preferably, further control is as follows: , the formula and formula (23) United, when At that time, it can be obtained ,Right now:

[0136]

[0137] Formula (24) shows that, in the processing spot diameter Given a fixed value, if it is desired that the pulse coverage density in the scanning direction is consistent with the coverage density of the adjacent transverse scan lines, then the scan line spacing... The preferred setting is the center spacing between adjacent pulses. ,Right now Through the above matching control, an approximately consistent pulse spatial distribution density can be obtained in two orthogonal directions within a unit area, thereby making the surface energy deposition more uniform and helping to reduce local over-ablation, under-ablation, and streak residue caused by directional superposition differences.

[0138] Determining the pulse overlap rate overlap with scan lines Subsequently, a vertical cross-scanning strategy was further established. Vertical cross-scanning refers to the main scanning directions of two adjacent scanning layers being perpendicular to each other. One scanning layer performs a parallel line scan along the X direction, and the next scanning layer performs a parallel line scan along the Y direction, thereby forming an orthogonal energy coverage network on the surface to be processed.

[0139] In one embodiment, if the first layer is scanned along the X-axis, then the second layer is scanned along the Y-axis; if the third layer is again scanned along the X-axis, then the fourth layer is scanned along the Y-axis, and so on. Odd-numbered layers are defined as scanning layers along the X-axis, and even-numbered layers are defined as scanning layers along the Y-axis. Preferably, after each unidirectional scan is completed, the workpiece coordinate system or the galvanometer scanning coordinate system is rotated. This ensures that the scanning direction of the next layer is strictly perpendicular to that of the previous layer.

[0140] In this embodiment, a set of unidirectional scanning layers along the X direction and a set of unidirectional scanning layers along the Y direction constitute a complete set of orthogonal scanning layers, defined as "one vertical cross-scan" or "one set of vertical cross-scans". In other words, completing the X-direction scan followed by the Y-direction scan can be counted as one processing cycle. This definition facilitates the establishment of processing rounds, cumulative scan counts, and removal amount feedback control logic in subsequent step 4, using "removal depth of a single vertical cross-scan" as the unit. Compared to the parallel scanning method in a single direction, this embodiment uses alternating vertical cross-scans in the X and Y directions, which can make the material removal in different directions more balanced, reducing the directional texture formed on the surface due to repeated ablation in a single direction; it can allow local peaks to repeatedly receive energy in different directions, thereby improving the peak reduction and flattening effect; and in terms of control... and Under equal or approximately equal conditions, the pulse coverage density per unit area can be made to be consistent in both directions, thereby further improving the removal uniformity and surface morphology convergence; it can provide a more stable surface evolution basis for roughness feedback control in the subsequent step 4, and avoid the true surface quality change trend being masked by unidirectional scanning texture.

[0141] In practice, the main control computer 10 determines the processing spot diameter obtained in step 2. Preset laser repetition frequency Target scanning speed Spacing between the target scan line and the target scan line First, calculate the pulse overlap rate. overlap with scan line When the calculation result does not meet the preset matching conditions, the main control computer adjusts the scanning speed. and / or scan line spacing Make corrections until the requirements are met. or .in, To allow for deviation, the value can be set according to the equipment control precision and process requirements, for example, 0.01-0.05. After correction, the main control computer 10 drives the galvanometer scanning head 5 to perform scanning sequentially in the manner of odd-numbered layers along the X direction and even-numbered layers along the Y direction, and completes the step-by-step splicing of large areas through the precision linear displacement module 8 to achieve continuous and uniform coverage of the surface to be processed.

[0142] After processing in step 3, the system output parameters and control results include: pulse overlap rate. Scan line overlap rate ;satisfy Or scanning speed under approximately equal conditions Spacing between scan lines Alternating vertical cross-scanning paths in the X and Y directions; definition of a single vertical cross-scan. The single vertical cross-scan serves as the processing unit for subsequent step 4, including single-scan depth determination, setting the number of basic scan groups, and dynamic iterative control.

[0143] Step 4: Set the target cumulative removal depth based on the initial maximum height difference. Determine the theoretical total number of scans based on the removal depth of a single vertical cross scan. Determine the number of scans per round of processing based on the working condition type corresponding to the initial maximum height difference. After the nth round of processing, obtain the current cumulative removal depth and the current arithmetic mean roughness. Compare the current arithmetic mean roughness with the reference roughness of the (n-1)th round, and compare the current cumulative removal depth with the target cumulative removal depth. When the current arithmetic mean roughness > the reference roughness and the current cumulative removal depth > the target cumulative removal depth, update the degradation counter. When the current arithmetic mean roughness ≤ the reference roughness, reset the degradation counter and update the historical best roughness and the reference roughness. Determine whether to stop processing or enter the next iteration based on the degradation counter result and / or the roughness convergence result.

[0144] Step 4 includes:

[0145] Step 4.1: Set the target cumulative removal depth based on the initial maximum height difference, so that the target cumulative removal depth has a safety margin on the basis of covering the initial maximum height difference, and the target cumulative removal depth is 1.5 to 2.0 times the initial maximum height difference.

[0146] The purpose of step 4.1 is to determine the initial maximum height difference of the surface to be processed based on the measurement in step 1. To set a reasonable target cumulative removal depth for subsequent multiple rounds of vertical cross-scanning processing. This ensures that the amount of material removed afterward can not only cover the maximum peak-valley difference on the initial surface, but also reserve an appropriate safety margin on this basis, thereby ensuring that deep valley defects are fully removed, while avoiding obvious peak-valley undulations remaining on the surface due to insufficient removal amount.

[0147] In this embodiment, the target cumulative removal depth This refers to the total thickness that is expected to be removed in the normal direction of the surface to be processed from the start to the end of laser processing. The removal depth is the normal retreat distance of the processed surface relative to the original reference surface before processing. In other words, It is the depth control benchmark used in step 4 to measure whether the overall processing has achieved the expected flattening target.

[0148] Due to the initial maximum height difference defined in step 1 It represents the vertical height difference between the highest peak and the lowest valley within the same measurement area, therefore It can directly reflect the maximum amplitude of the initial peak-valley undulations of the surface to be processed. If the subsequent cumulative removal depth is less than or equal to... However, the following situations may still exist during processing: First, some deep valley areas may not be completely covered; second, there may be spatial non-uniformity in material removal, resulting in insufficient actual flattening of some peak and valley areas; third, measurement errors, surface fluctuations, and scanning superposition deviations may cause local residual undulations. Therefore, this application does not simply set the target cumulative removal depth as equal to... Equal, but in On the basis of this, a safety margin is added to improve the stability and adequacy of macro-leveling.

[0149] In this embodiment, the cumulative removal depth of the target Set it according to the following formula:

[0150]

[0151] In the formula: This refers to the initial maximum height difference measured in step 1; This is a safety factor. Preferably, the safety factor... The value range is from 1.5 to 2.0, therefore the cumulative removal depth of the target satisfies:

[0152]

[0153] Among them: when When, it indicates that a 50% safety margin is reserved based on the initial maximum height difference; when When the cumulative removal depth of the target is twice the initial maximum height difference, it indicates that the target cumulative removal depth is twice the initial maximum height difference.

[0154] Therefore, the cumulative removal depth is not a fixed value, but rather adapts to the initial peak-to-valley difference on the surface to be processed. For workpieces with large initial surface undulations, If it is larger, then The corresponding increase; for workpieces with a relatively smooth initial surface, Smaller, then The corresponding reduction allows the subsequent machining depth to match the initial shape of the workpiece.

[0155] In this embodiment, the safety factor The setting of 1.5 to 2.0 is mainly based on the following considerations: When When the cumulative removal depth is insufficient relative to the initial maximum height difference, it may be difficult to completely remove deep valley defects in actual processing, especially for cases with uneven peak-valley distribution, concentrated local deep valleys, or strong random undulations on the surface of additively manufactured metal parts. This can easily lead to the presence of deep valley areas remaining on the surface, thus affecting the final flatness. While theoretically this could further increase the sufficiency of removal, it would significantly increase the total number of scans and processing time, resulting in a decrease in processing efficiency. It would also increase the risk of energy accumulation and heat accumulation, thereby increasing the possibility of surface overcutting, local melting, or expansion of the heat-affected zone.

[0156] Therefore, this application limits the target cumulative removal depth to within the range of 1.5 to 2.0 times the initial maximum height difference, achieving a balance between sufficient removal and processing economy. On the one hand, the target cumulative removal depth can cover the original peak-valley span and compensate for possible local removal unevenness during processing; on the other hand, it can avoid unnecessary processing redundancy caused by setting the target removal depth too large. In this way, step 4.1 provides a unified and quantifiable depth control benchmark for subsequent scan group calculation, scan count setting per round, and processing termination judgment.

[0157] In one embodiment, when step 1 identifies the surface to be processed as being in a large-scale removal condition, since this type of condition typically corresponds to a large amount of material removal... The result calculated using the above formula is... The corresponding size is also relatively large to ensure that subsequent multiple scans can fully remove surface peaks and cover deep valley areas; when step 1 identifies the surface to be processed as being in a fine homogenization condition, since this type of condition corresponds to a smaller... The calculated result The depth is also correspondingly smaller, thus avoiding overcutting due to an excessively large target depth setting when the initial surface is already relatively flat. Therefore, in step 4.1... The settings and the working condition identification results in step 1 are logically related and together form the deep foundation for subsequent dynamic iterative control.

[0158] In actual execution, the main control computer 10 receives the initial maximum height difference output in step 1. And according to the preset safety factor Automatically calculate the cumulative removal depth of the target The calculation results are stored in the control system and serve as the benchmark values ​​for calculating the basic scan group number in step 4.2 and for determining the depth compliance in step 4.3. After each subsequent processing cycle, the current cumulative removal depth is measured. and By comparison, it can be determined whether the current processing has approached or reached the predetermined depth target.

[0159] After processing in step 4.1, the system should output at least the following parameters: initial maximum height difference. Safety factor Target cumulative removal depth Among them, the target cumulative removal depth It serves as the core depth benchmark for subsequent scanning group setting, depth attainment determination, and processing termination control.

[0160] Step 4.2: Based on the removal depth of a single vertical cross-scan Cumulative removal depth with target Calculate the number of basic scan groups The number of scans per processing cycle is dynamically configured based on the large-scale removal or fine homogenization conditions characterized by the initial maximum height difference. .

[0161] The purpose of step 4.2 is to estimate the number of basic scan groups required to achieve the target cumulative removal depth based on the actual removal capacity of a single vertical cross-scan on the surface to be processed, and to combine this with the initial maximum height difference from step 1. The type of working condition is represented, and the number of scans for each subsequent processing round is dynamically configured, so as to ensure the achievability of processing depth while taking into account processing efficiency and surface finishing accuracy.

[0162] In this embodiment, the removal depth of a single vertical cross-scan This refers to using a predetermined processing spot diameter under the scanning strategy constructed in step 3. Laser repetition frequency Scanning speed Scan line spacing Pulse overlap rate Scan line overlap rate and average output power The average material removal depth is the result of one vertical cross-scan of the surface to be processed. "One vertical cross-scan" refers to a combined processing unit that completes one scan along the X direction and then another scan along the Y direction. Removal Depth It is neither the depth of a single pulse pit nor the depth of a single-layer scan in a single direction, but rather the average normal removal amount corresponding to orthogonal double-layer scan as the basic processing unit.

[0163] In one embodiment, a single vertical cross-scan removes depth. This can be obtained through preliminary experiments. Specifically, a sample with the same material or similar surface condition as the actual workpiece to be processed can be selected. Under the processing parameters determined in steps 2 and 3, a single vertical cross-scan is performed. Then, the height of the same measurement area before and after processing is compared using a three-dimensional surface profilometer 9, and the average removal depth is calculated. Preferably, measurements can be repeated at multiple locations and the average value taken to reduce the influence of local fluctuations on the results. If the change in normal distance between the reference average surface before processing and the reference average surface after processing is used to characterize the amount of material removed, then this average distance change can be used as the removal depth of a single vertical cross-scan. To improve control precision, It is preferred that the measurements be taken under the same conditions as the subsequent formal processing, including defocusing amount, power, repetition rate, overlap rate, and scanning strategy.

[0164] In this embodiment, the basic number of scan groups Under ideal average removal conditions, the cumulative removal depth is the distance to be removed in order to achieve the target. The theoretically required minimum number of vertical cross-scans. Essentially, it's an estimate based on average removal capacity, used to provide an initial processing scale reference for subsequent dynamic iterative control. The cumulative removal depth of the known target... Depth removal by single vertical cross-scan Under the premise of, the number of basic scan groups Calculate using the following formula:

[0165]

[0166] In the formula: This represents the floor function, i.e., when... When the value is not an integer, the smallest integer greater than or equal to that value is used. The purpose of rounding up is to ensure that the theoretical cumulative removal amount is not less than the target cumulative removal depth, thereby avoiding insufficient theoretical processing due to simple rounding or rounding down. For example, when... hour, This means that at least 8 vertical cross scans are required to theoretically reach or exceed the target cumulative removal depth.

[0167] It should be noted that the number of basic scan groups This is not equivalent to the fixed total number of scans performed subsequently, but rather a theoretical reference value used in step 4.2 to establish the initial processing scale. Because material removal behavior during actual processing is affected by factors such as local morphological fluctuations, heat accumulation, surface quality evolution, and changes in processing efficiency across different rounds, this application does not simply perform the process in a single step. Stop immediately after the first scan, instead using... Based on the theoretical foundation, the number of scans per round is further dynamically set according to the type of working condition. And in subsequent step 4.3, it is corrected round by round through feedback control.

[0168] In this embodiment, the number of scans per processing round In dynamic iterative control, this refers to the number of consecutive vertical cross-scans performed each time a new processing stage is entered. In other words, It represents the number of scan groups executed by the system within a closed-loop cycle of processing, pausing, detection, and judgment, and is an important control parameter for the subsequent processing step size.

[0169] like A larger value results in a larger cumulative removal amount per processing stage and higher single-stage processing efficiency, but a relatively lower frequency of stage-based detection; if... Smaller values ​​allow the system to perform surface quality checks and condition corrections more frequently, but result in a slower processing cycle. Therefore, The proper configuration directly affects the efficiency of the large excess removal stage and the overcut control capability of the fine homogenization stage.

[0170] This application does not apply a fixed method to all surfaces to be processed. Instead, it is based on the initial maximum height difference in step 1. The operating condition type represented is dynamically configured. Specifically, step 1 has been based on... The surfaces to be processed are divided into "large-scale removal" and "fine homogenization" conditions. Because the two conditions differ significantly in initial peak-to-valley differences, removal targets, and risk control requirements, the number of scans per processing round is determined accordingly. They should also be set differently.

[0171] When step 1 identifies the surface to be processed as being in a condition of large allowance removal, it indicates that the initial maximum height difference of the surface to be processed is... The surface is relatively large, exhibiting obvious peaks and valleys, and has a significant material allowance. For this type of working condition, it is preferable to... Setting this value to a larger value improves single-round processing efficiency, accelerates surface peak removal speed, and approaches the target cumulative removal depth more quickly. In one embodiment, for large-scale removal, the number of scans per round of processing can be increased. Set to 6-20 times, preferably select Next. By adopting a larger This can reduce cycle time loss caused by frequent machine downtime for testing and improve processing efficiency during the large margin stage.

[0172] When step 1 identifies the surface to be processed as being in a finely homogenized state, it indicates that the initial maximum height difference of the surface to be processed is... The surface is relatively small and close to being smoothed; the focus of subsequent processing shifts from rapid removal to suppressing overcutting and improving surface convergence. For this type of condition, it is preferable to... Setting the value to a smaller value allows the system to pause detection after a short processing step, thus promptly identifying trends of improvement, stagnation, or deterioration in surface roughness and preventing localized over-removal due to excessive single-round scans. In one embodiment, for fine homogenization conditions, the number of scans per processing round can be... Set to 1-5 times, preferably select Second-rate.

[0173] Therefore, in this embodiment The configuration logic is not fixed-step processing, but based on the initial maximum height difference. Different step sizes are selected based on the degree of surface undulation: for working conditions with large surface undulations and sufficient margin, a larger step size is used. To enhance efficiency; for working conditions with small surface undulations and close to the finishing endpoint, a smaller [size / size] is used. To enhance accuracy. This adaptive step size configuration allows step 4.2 to switch the processing rhythm in a targeted manner between the large allowance processing stage and the fine convergence stage, rather than using a uniform and coarse control method throughout the process.

[0174] It should be noted that the number of basic scan groups Number of scans per processing round They are functionally related but not identical. Used to represent the total scan size theoretically required to achieve the target cumulative removal depth; This is used to represent the processing step size in each round of dynamic iteration. The former is a predicted parameter at the overall goal level, while the latter is an execution parameter at the round control level.

[0175] In practice, the main control computer 10 first uses formula (27) to... The theoretical baseline scan group number is calculated, and then the corresponding operating condition type is assigned to the system based on the operating condition type identified in step 1. value, and the The number of scans for the first round of processing plan in subsequent step 4.3 The initial value. In other words, we can let This serves as the planned number of scans for the first round of processing, and then, based on surface quality feedback after each round of processing, a decision is made on whether to increase the number further. Proceed to the next round.

[0176] Through step 4.2 above, this application removes depth by introducing a single vertical cross-scan. and base scan group number This allows the target to be cumulatively removed in depth. This can be converted into executable scan count parameters, thereby establishing a quantitative correspondence between target depth, single-scan removal capacity, and theoretical total scan size; by relying on the initial maximum height difference The dynamic configuration of the represented working condition type This enables the system to maintain high efficiency during the large-scale removal stage and improves the detection frequency and control accuracy during the fine homogenization stage; by... and The layered setup provides sufficient adjustment space for the closed-loop feedback control in the subsequent step 4.3, avoiding the risks of insufficient or over-processing caused by processing only once based on a fixed total number of scans.

[0177] After processing in step 4.2, the system output parameters include: single vertical cross-scan removal depth. Basic scan group number Number of scans per processing round Number of scans in the first round of planning .in, As a reference for the overall theoretical processing scale and This serves as the execution parameter for the dynamic iterative processing and phased detection in step 4.3.

[0178] Step 4.3: First, initialize the first round of planned scan count, surface roughness baseline value, degradation counter, historical best roughness, and convergence threshold, then... After the machining cycle is completed, the current cumulative removal depth and the current arithmetic mean roughness are obtained. Based on the change of the current arithmetic mean roughness relative to the previous reference roughness and the achievement of the current cumulative removal depth relative to the target cumulative removal depth, the degradation counter, historical best roughness and reference roughness are updated to establish an iterative execution and feedback control process.

[0179] In this embodiment, the main state variables involved in step 4.3 include: the number of planned scans in the current round. Previous round of surface roughness reference value Current round measured arithmetic mean roughness Current cumulative removal depth Deterioration counter Historical best roughness and convergence threshold .in, Used to indicate the actual number of vertical cross scans performed in the current processing round; Used to represent the surface roughness reference value of the previous round before entering the current round of judgment; Used to represent the arithmetic mean roughness measured after the current wheel is machined; Used to indicate the cumulative removal depth from the start of processing to the end of the current cycle; Used to record the number of times quality deteriorates consecutively after the depth approaches or reaches the target. Used to record the optimal roughness value obtained throughout the entire machining process; The threshold used to characterize whether the roughness change has entered a convergent or stagnant state. As can be seen from the variables above, step 4.3 identifies the surface evolution trend through multivariate collaborative updating.

[0180] Before officially entering the first round of processing, the system first performs a round 0 state initialization to establish the initial baseline for subsequent round-by-round comparisons and feedback updates. Specifically, the main control computer 10 performs the following initialization operations: setting the number of planned scans for the first round to [number missing]. ,in, For step 4.2, configure the number of machining scans per round according to the working condition type; and use the initial arithmetic mean roughness measured in step 1. As the initial reference roughness, it is set to Initialize the deterioration counter to Initialize the historical best roughness to the current initial roughness, that is... Set roughness convergence threshold Preferably, The value range is 3%-5%. Through the above initialization, the surface quality in the unprocessed state is used as the comparison benchmark for the effect of the first round of processing, and a quality trend judgment reference system shared by all subsequent rounds is established.

[0181] After initialization is complete, the system enters the next step. Wheel machining, among which In the first During the wheel machining process, the main control computer 10 controls the ultrafast laser 1, the galvanometer scanning head 5, and the precision linear displacement module 8 to execute the scanning strategy constructed in step 3. Secondary vertical cross-scan. It should be noted that here... This does not represent the total cumulative number of scans, but rather the number of scans performed in a single operation within the closed-loop cycle of processing, pausing, detecting, and judging in this round. (Complete this...) After the first vertical cross-scan, the system pauses processing and enters a phased inspection.

[0182] In the After the wheel machining is completed, the surface morphology of the current machining area is measured using a 3D surface profilometer 9, and the following two key feedback quantities are obtained through the main control computer 10: current cumulative removal depth. and the current arithmetic mean roughness Among them, the current cumulative removal depth Indicates from the start of processing to the [number]th [stage]. The total normal removal amount of the workpiece surface relative to the initial reference surface at the end of the wheel rotation; the current arithmetic mean roughness. This indicates the average surface roughness within the measurement area under the current processing condition.

[0183] In obtaining the first Wheel and Then, the main control computer 10 evaluates the current state. The evaluation logic includes two dimensions: first, comparing the current roughness. Compared with the previous reference roughness First, the magnitude of the difference in surface quality is used to determine whether the surface quality is improving, remaining the same, or deteriorating. Second, the current cumulative removal depth is compared. Cumulative removal depth with target The relationship between these two dimensions is used to determine whether the current processing has reached the target depth stage. This dual-dimensional linkage judgment differs from control methods that only look at roughness changes or only look at removal depth changes. Its core is that: the same roughness deterioration can be regarded as normal fluctuation before the target depth is reached; but after the target depth has been reached or is close to being reached, it should be regarded as a potential over-processing degradation signal.

[0184] When detected This indicates that the surface roughness after the current processing round is greater than the baseline value of the previous round, meaning the surface quality is deteriorating. At this point, the system further adjusts the current cumulative removal depth... Has the target cumulative removal depth been reached? To determine the branch.

[0185] Furthermore, if the following conditions are met Alternatively, in actual engineering implementation, an equivalent judgment of "close to meeting the standard" can be adopted, for example... This indicates that the current removal depth has reached or is close to the predetermined target, but the roughness has begun to deteriorate. At this point, this degradation can be considered "true quality degradation after reaching the target depth," and the degradation counter can be cumulatively updated. Only when the depth objective has been largely achieved can the continued deterioration of roughness be considered a meaningful termination warning signal.

[0186] Conversely, if satisfying This indicates that the current processing depth has not yet reached the predetermined target. Even if an increase in roughness is detected in this round, it can be considered a process fluctuation during the stage where the depth has not reached the target, rather than an immediate basis for termination. Therefore, in this case, the deterioration counter remains unchanged. In other words, before the target depth is reached, this application allows for local and transient roughness fluctuations during the processing without immediately interrupting the processing due to a single fluctuation, thereby avoiding insufficient removal caused by premature termination.

[0187] Given the current deterioration in surface roughness, to prevent amplified errors in the trend judgment of the next round caused by abnormal fluctuations in a single round, the surface roughness reference value... A conservative update approach is preferred. Specifically, any of the following approaches can be used:

[0188] Method 1 is to maintain The method remains unchanged; the second method is based on... Update method. When an abnormal deterioration occurs in a certain round but the termination condition has not yet been met, the system does not immediately use the deteriorated measured value as the new comparison benchmark, so as to avoid distortion of subsequent rate of change calculation and trend judgment due to a single outlier.

[0189] When detected If the current condition is positive, it indicates that the surface roughness after the current machining cycle has not deteriorated compared to the baseline value of the previous cycle, meaning it is in an improved or stable state. In this case, the system determines that the current machining state is healthy and should perform a positive update on the main state variables.

[0190] First, reset the deterioration counter to zero, that is... Once the surface quality recovers or remains unchanged, it indicates that the previous possible deterioration trend did not continue, and therefore the continuous degradation count should be reset.

[0191] Secondly, the current roughness Compared with historical best roughness Compare, if satisfied This indicates that the current processing yielded the best surface quality to date, therefore the updated historical best roughness is [value missing]. ;like Then keep Unchanged. By retaining the optimal roughness record throughout the entire processing, the system can backtrack to the obtained optimal surface state as a result reference when subsequent continuous degradation triggers termination.

[0192] Furthermore, if the current surface roughness improves or remains unchanged, the current measured surface roughness will be used as the benchmark value for the next round of judgment. When the surface quality evolution is in a healthy direction, the system allows the current measurement results to be incorporated into the baseline update, enabling subsequent comparisons to truly reflect the improvement trend between adjacent rounds.

[0193] Based on the above state evaluation and variable update, step 4.3 establishes the following iterative execution and feedback control flow: Initialize the state of round 0, set... , , , and ; Enter the Wheel machining, execution Secondary vertical cross-scan; pause processing, measure and acquire. and ;Will and Compare, and at the same time and Compare; update based on comparison results , and The updated state variables are used as the basis for the next round of judgment, leading to subsequent termination condition judgments or the next iteration. Thus, the system forms a closed-loop feedback control mechanism of processing, detection, judgment, updating, and reprocessing, enabling the processing to no longer rely on a preset fixed total number of scans, but to dynamically advance based on the actual surface quality evolution and the completion of the target depth.

[0194] Step 4.3 By jointly judging the current roughness change with the current cumulative removal depth attainment status, it avoids misjudging transient roughness fluctuations in the depth-deficient stage as termination signals, thereby preventing premature stopping of processing; after reaching or approaching the target depth, it can promptly identify the continuous quality degradation trend, thus providing a basis for subsequent protective termination; by introducing Recording historical best surface quality ensures the system retains an optimal reference state even when degradation occurs later in the processing phase; this is achieved by introducing... The conservative update mechanism improves the robustness of trend comparison between rounds and reduces the interference of a single abnormal measurement on the overall control logic.

[0195] After step 4.3 is executed, the system outputs the following status variables: current cumulative removal depth. Current arithmetic mean roughness Updated deterioration counter Updated historical best roughness Updated surface roughness reference value The state variables are used in step 4.4 to execute the persistent degradation protection criterion and the accuracy convergence criterion.

[0196] Step 4.4: Determine the termination condition based on the deterioration counter and the relative change rate of surface roughness. When quality deterioration occurs in two consecutive rounds and the current cumulative removal depth reaches or approaches the target cumulative removal depth, or when the relative change rate of surface roughness is less than the preset convergence threshold and the current cumulative removal depth reaches or approaches the target cumulative removal depth, or when the relative change rate of surface roughness in two consecutive rounds is less than the convergence threshold, terminate the processing and retain the historical best roughness state as the final result. Otherwise, increase the cumulative planned scan count and enter the next iteration.

[0197] In this embodiment, step 4.4 employs two types of termination criteria: the first is a continuous degradation protection criterion, used to identify whether the surface quality continuously degrades after the cumulative removal depth of the target has been reached or is close to being reached; the second is a precision convergence criterion, used to identify whether the surface roughness improvement has entered a convergence or stagnant state. If either of these two criteria is met, the system determines that the processing should terminate; if neither criterion is met, the next iteration continues.

[0198] In one embodiment, the system first updates the deterioration counter based on the result obtained in step 4.3. Determine if continuous quality degradation has occurred. Two consecutive rounds of quality degradation refer to a situation where, in two adjacent rounds of state assessment, the current arithmetic mean roughness... Compared to the previous reference roughness All show signs of deterioration, and the corresponding deterioration counters accumulate to a preset threshold. Preferably, the persistent degradation threshold is set to 2, that is, when... At that time, it was determined that the surface had deteriorated in quality for two consecutive rounds.

[0199] However, this application does not immediately terminate processing after two consecutive rounds of deterioration, but rather further determines the current cumulative removal depth. Has the target cumulative removal depth been reached or is it close to being reached? Preferably, any of the following forms can be used as the criterion for "depth reaching or nearing the standard": or ,in, This indicates that the current cumulative removal depth has reached more than 90% of the target cumulative removal depth, which can be regarded as an engineering equivalent criterion for "approaching the target cumulative removal depth".

[0200] Therefore, when both conditions are met and The system determines that the current processing has entered a stage of continuous quality degradation. At this stage, even increasing the number of scans will not further improve surface quality; instead, over-processing may lead to continued deterioration of surface roughness, localized overcutting, or accumulation of thermal effects. Therefore, the main control computer 10 immediately issues a termination command to stop processing and outputs an alarm signal, while retaining the historical best surface roughness. The corresponding processing state is taken as the final result.

[0201] In addition to protection against continuous deterioration, this embodiment also utilizes the relative change rate of surface roughness. Determine whether the machining process has entered the convergence or stagnation stage. The relative rate of change of surface roughness refers to the relative decrease in the roughness of the current wheel compared to the reference roughness of the previous wheel. Its calculation formula is:

[0202]

[0203] In the formula: The surface roughness reference value from the previous round before entering this round of judgment; This represents the current arithmetic mean roughness obtained in this round of testing. When When the value is large, it indicates that the surface roughness has decreased significantly after this round of processing, and the surface quality is still effectively improving; when When the value is small, it indicates that the roughness improvement brought about by this round of processing is limited, and the surface quality tends to converge or stagnate.

[0204] It should be noted that in the formula This is not necessarily equal to the roughness value actually measured in the previous round, but rather the baseline value updated in step 4.3. In other words, if the previous round determined the quality to be improved or unchanged, then... The data has been updated to the measured values ​​from the previous round; if the previous round determined that the quality had deteriorated but had not yet triggered termination, then... The baseline value before the deterioration can be kept unchanged, or a conservative update method can be used. Therefore, In reality, it reflects the improvement in roughness relative to the current effective benchmark, rather than mechanically reflecting the difference between adjacent measured values. This design improves the stability and robustness of the rate of change assessment.

[0205] In this embodiment, the convergence threshold of the surface roughness change is denoted as... Preferably, The value range is 3%-5%, that is ,when When the current machining process has improved the surface roughness by less than the preset minimum effective improvement threshold, it can be considered that the machining effect is converging or has entered a stagnant phase; when When the current wheel machining is in operation, it indicates that the current wheel machining can still bring about significant roughness improvement, and the machining is still in the effective removal stage.

[0206] Furthermore, regarding convergence termination under the depth-achieved condition. When the system detects... And simultaneously satisfy When the current cumulative removal depth has reached or is close to the target cumulative removal depth, and the improvement in surface roughness is less than the preset convergence threshold, it can be considered that: on the one hand, the material removal target has been basically achieved; on the other hand, the marginal contribution of continued processing to reducing surface roughness is very small. Therefore, the system determines that the processing process has reached a convergence state and immediately issues a termination command to stop processing.

[0207] Regarding early termination under conditions of continuous stagnation despite insufficient depth: In some cases, although the current cumulative removal depth... The target cumulative removal depth has not yet been reached. However, surface roughness improvement has already stalled prematurely. To avoid wasting resources by continuing processing in such cases, this application further sets up a logic for early termination of continuous stalling. Specifically, if two consecutive rounds meet the following conditions: If the relative change rate of surface roughness is less than the convergence threshold for two consecutive rounds, it can be determined that the processing process has entered an ineffective stagnation period.

[0208] In one embodiment, this can be achieved by setting a stall counter or recording two consecutive rounds in the control program. The system determines the surface roughness based on the current state of the surface. Even if the theoretical depth target has not been fully achieved, if two consecutive rounds of processing fail to bring sufficient surface quality improvement, it indicates that the marginal benefit of continuing processing under the current process conditions is extremely low. Increasing the number of scans not only fails to significantly improve surface quality but may also lead to over-processing, heat accumulation, or reduced efficiency. Therefore, in this situation, the system also issues a termination command to stop processing and retains the historical best roughness. The corresponding state is taken as the final result.

[0209] When either the persistent degradation protection criterion or the accuracy convergence criterion is met, the system terminates the current machining process and retains the historical best roughness. The corresponding state is used as the final result. Retaining the historical best surface roughness corresponds to the optimal surface quality achieved throughout the entire processing process, rather than simply using the roughness measured in the last round as the final result. In the later stages of processing, the surface quality may slightly rebound or degrade after reaching its optimal value. If only the last round's measurement value is used as the result, it may not truly reflect the optimal surface state achievable by this process. By retaining... In the corresponding state, the system can ensure that the final result is not degraded by overprocessing at the end or slight fluctuations.

[0210] If neither of the above two termination criteria is met, it indicates that the current processing is still in the effective removal stage, or although there are local fluctuations, the conditions for stopping processing have not yet been met. At this time, the main control computer 10 executes the next round of iteration preparation operation, increases the cumulative planned scan count, and returns to the processing, detection, and judgment process in step 4.3 to continue the next round of processing.

[0211] In one embodiment, it can be pressed The following method updates the cumulative planned scan count, where, This refers to the number of scans per round of machining preset according to the working condition type in step 4.2. (Updated) For the A new number of vertical cross scans are performed during wheel machining.

[0212] Therefore, this application establishes a clear logical relationship between termination, retaining the optimal result, and continuing iteration through step 4.4: when continuous degradation occurs and the depth has reached or is close to reaching the target, the process is terminated immediately to protect surface quality; when roughness improvement enters a convergence or continuous stagnation stage, the process is terminated to avoid invalid processing; when none of the above situations occur, the processing is determined to be effective, the cumulative planned scan count is increased, and the next iteration begins. Thus, the entire step 4 constitutes a dynamic closed-loop control system with the target removal depth as a constraint and the surface quality trend as the core.

[0213] After the judgment in step 4.4, the system output control results include: terminating processing and retaining the historical best roughness corresponding state; increasing the cumulative planned scan count and entering the next iteration. Simultaneously, the system output auxiliary status information includes: the current deterioration counter. Current relative change rate of surface roughness Current cumulative removal depth Cumulative removal depth with target The comparison results; the determination results of whether the current stage has entered a continuous degradation stage, a convergence stage, or a stagnation stage.

[0214] Example

[0215] This embodiment uses an Fe-Cr-Ni based alloy steel workpiece manufactured by SLM as the object, and performs surface finishing using the ultrafast laser processing method for metal workpieces based on surface quality feedback described in this invention. The laser used is a femtosecond laser with an output wavelength of 343±2nm, an output pulse width ≤300fs, a maximum single pulse energy ≥20μJ, a repetition frequency of 100-500kHz, and a beam quality... .

[0216] Step 1: Surface Pretreatment and Initial Morphology Characterization. First, the SLM-formed workpiece was sequentially ultrasonically cleaned for 5 minutes each in anhydrous ethanol and deionized water, followed by drying. The surface to be processed was the side of the additively manufactured workpiece, i.e., the surface parallel to the forming direction. After pretreatment, the metal workpiece was fixed on a fixture, and the surface to be processed was moved to the initial morphology measurement position using a precision linear displacement module. A 3D surface profilometer was used to measure the surface area of ​​1.75... 1.32 A surface scan was performed on the area to be processed, yielding an initial maximum height difference of 112.8. The initial arithmetic mean roughness is 10.2. .because >80 Therefore, the current surface to be processed is determined to be a large amount of material removal condition, and a "fast peak shaving mode" is matched, that is, a higher single pulse energy density and a faster scanning speed are subsequently used.

[0217] Step S2: Calculation of spot parameters and power setting based on defocus effect. First, the single-pulse ablation threshold is determined on the surface of a pretreated sample of the same material using the recognized area extrapolation method. The diameter of the ablation pit under different single-pulse energy conditions is observed under a microscope and fitted to obtain the single-pulse ablation threshold of the material under the current femtosecond laser conditions. The laser wavelength is 345 nm, and the pulse width is 300 fs. If the single-pulse ablation threshold of the metal material to be processed is known, this threshold determination step can be omitted. Next, the process defocusing amount is set. Given the laser beam waist radius laser wavelength Rayleigh length The radius of the light spot at the out-of-focus position is determined by... After calculation and substituting the parameters, the radius of the light spot at the defocus position is approximately... Then the diameter of the processing spot Finally, the laser repetition frequency is set. Safety factor ,according to Calculate the required average output power At this point, the energy density of the processed surface is That is, the peak energy density at the center of the defocused processing surface is slightly higher than the single-pulse ablation threshold of the material, thus enabling stable and controllable material removal.

[0218] Step 3: Scanning strategy construction and overlap rate control. Set the galvanometer scanning speed. Scan line spacing Based on the diameter of the processing spot and laser repetition frequency The distance between the centers of adjacent pulses is The corresponding pulse overlap rate is The scan line overlap rate is Therefore, we can conclude that... Under these conditions, a vertical cross-scanning method alternating between the X and Y directions is used for processing. That is, the first layer is scanned along the X-axis, the second layer is scanned along the Y-axis, and subsequent layers are scanned alternately in the X and Y directions. Completing one set of X and Y orthogonal scans constitutes one processing cycle.

[0219] Step 4: Dynamic iterative control based on surface quality feedback. First, based on the initial maximum height difference... Set target cumulative removal depth In this embodiment, a safety factor is used. ,but The average removal depth of a single vertical cross-scan was measured through preliminary experiments. Then the number of basic scan groups is Since the current process involves removing a large amount of excess material, the number of scans per processing cycle is set to ensure processing efficiency. Each round of processing involves 10 sets of vertical cross-scans. A closed-loop control process is then established: initializing the planned number of scans for the first round. Set the surface roughness reference value Initialize the degradation counter Historical best roughness And the convergence threshold Set to 3%.

[0220] In the first round of processing, 10 sets of vertical cross-scans were performed according to the processing parameters to detect the current arithmetic mean roughness. Current cumulative removal depth . judge (10.2) and (180.5) Determine if surface quality has improved, reset the deterioration counter. Update historical best roughness And update the reference roughness to .at this time , It is expected to require no more than 5 rounds of processing.

[0221] In the second round of processing, 10 sets of vertical cross-scans were performed according to the processing parameters to detect... , ,judge (8.8) and (180.5) Similarly, as the roughness continues to decrease, the surface quality improves, but the cumulative removal depth has not yet reached the target value, so processing continues.

[0222] In the third round of processing, 10 sets of vertical cross-scans were performed according to the processing parameters to detect... , ,judge (7.8) and (180.5) The surface quality is still determined to be improved and the cumulative removal depth has not yet reached the target value, so processing continues.

[0223] In the fourth round of processing, 10 sets of vertical cross-scans were performed according to the processing parameters to detect the results. , ,judge (5.4) and (180.5), at this point the cumulative removal depth has reached near the target value, and the surface roughness has further decreased, therefore update And proceed to the next round of testing.

[0224] In the fifth round of processing, 10 sets of vertical cross-scans were performed according to the processing parameters to detect the results. , , At this point, based on the relative rate of change of surface roughness Perform a convergence check when Furthermore, when the current cumulative removal depth reaches or approaches the target cumulative removal depth, the processing process is determined to have reached a convergence state. Set at 3%, The convergence was deemed successful. Further evaluation of the removal depth followed. Slightly smaller =180.5, which basically achieves the goal of removing depth. Judgment (4.6) The surface quality deteriorates, and Processing is stopped. Under the current scanning strategy, processing for 5 rounds, i.e., 50 perpendicular cross-processing cycles, can reduce the surface roughness from 10.2. Reduced to 5.1 The optimal number of machining passes is 4, i.e., 40 perpendicular cross-processing passes, which can reduce the surface roughness from 10.2. Reduced to 4.6 .

[0225] As per the instruction manual Figure 3 This figure shows the three-dimensional morphology of the surface of the unprocessed Fe-Cr-Ni based alloy steel workpiece manufactured by SLM in this embodiment. The color scale in the figure indicates that the surface height range is approximately -175.54. Up to 211.93 Different colors correspond to different surface heights, with warm-colored areas representing relatively raised areas and cool-colored areas representing relatively low-lying areas. As shown in the figure, the unprocessed surface exhibits significant overall undulation, with a chaotic and uneven distribution of peaks and valleys. Locally, there are prominent island-like and granular raised structures, accompanied by continuously distributed low-lying areas and valley morphologies, indicating strong surface height dispersion. This surface morphology reflects the typical raw surface characteristics of SLM-formed metal workpieces, indicating a large peak-valley difference and high roughness. Subsequent laser finishing is needed to smooth out the surface protrusions and improve overall uniformity.

[0226] As per the instruction manual Figure 4This figure shows the three-dimensional morphology of the workpiece surface after 40 vertical cross-scan finishing processes in this embodiment. Combining the color distribution and height scale in the figure, it can be seen that the overall undulation of the workpiece surface after finishing is significantly reduced compared to before processing. The previously prominent peak-like protrusions have been significantly weakened, and the surface height distribution tends to be more uniform. Large areas in the figure show a relatively continuous transitional morphology, without the distinctly isolated high-protrusion island structures seen before processing, indicating that vertical cross-scanning has a good peak-shaving and flattening effect on surface protrusions. At the same time, relatively fine directional interwoven textures can still be observed on the surface, indicating that the laser scanning trajectory has formed relatively uniform finishing marks on the surface. Overall, after 40 vertical cross-scan finishing processes, the peak-valley difference of the workpiece surface is effectively compressed, the surface roughness is significantly reduced, and both uniformity and flatness are improved.

[0227] As per the instruction manual Figure 5 This figure compares the surface morphology of the workpiece after 40 vertical cross-finishing processes in this embodiment with its original morphology. The upper and lower regions in the figure correspond to the finished surface and the unfinished original surface, respectively. Combining the color distribution and height scale, it can be seen that the surface undulations in the finished area are significantly reduced, and the overall morphology tends to be smoother and more uniform, while the original surface still exhibits large peak-valley fluctuations and relatively rough granular undulations. A clear morphology transition boundary is visible at the junction of the two regions, indicating that laser finishing has a significant reduction effect on surface protrusions. This comparison figure visually demonstrates that after 40 vertical cross-finishing processes, the peak-valley difference and roughness of the workpiece surface are significantly reduced, and the surface smoothness and consistency are significantly improved.

[0228] The above descriptions are merely embodiments of this application, and common knowledge regarding specific structures and characteristics in the solutions is not described in detail here. It will be apparent to those skilled in the art that this application is not limited to the details of the above exemplary embodiments, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Therefore, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for ultrafast laser processing of metal workpieces based on surface quality feedback, characterized in that, The method includes: Step 1: Pre-treat the surface of the metal workpiece, measure the initial maximum height difference and initial arithmetic mean roughness of the surface to be processed, and identify the working condition based on the initial maximum height difference to determine the laser removal strategy; Step 2: Determine the single-pulse ablation threshold of the metal material, calculate the size of the active spot and the diameter of the processing spot at the defocus position, and determine the average output power of the laser by combining the single-pulse ablation threshold, the laser repetition frequency and the active spot size; Step 3: Determine the pulse overlap rate and scan line overlap rate based on the processing spot diameter, laser repetition frequency, galvanometer scanning speed, and scan line spacing. Under the condition that the pulse overlap rate and scan line overlap rate are equal, use an alternating vertical cross-scanning method in the X and Y directions to process the surface to be processed. Step 4: Set the target cumulative removal depth based on the initial maximum height difference. Determine the theoretical total number of scans based on the removal depth of a single vertical cross scan. Determine the number of scans per round of processing based on the working condition type corresponding to the initial maximum height difference. After the nth round of processing, obtain the current cumulative removal depth and the current arithmetic mean roughness. Compare the current arithmetic mean roughness with the reference roughness of the (n-1)th round, and compare the current cumulative removal depth with the target cumulative removal depth. When the current arithmetic mean roughness > the reference roughness and the current cumulative removal depth > the target cumulative removal depth, update the degradation counter. When the current arithmetic mean roughness ≤ the reference roughness, reset the degradation counter and update the historical best roughness and the reference roughness. Determine whether to stop processing or enter the next iteration based on the degradation counter result and / or the roughness convergence result.

2. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 1, characterized in that, Step 4 includes: Step 4.1: Set the target cumulative removal depth based on the initial maximum height difference, so that the target cumulative removal depth has a safety margin on the basis of covering the initial maximum height difference, and the target cumulative removal depth is 1.5 to 2.0 times the initial maximum height difference; Target cumulative removal depth for: ； In the formula: This refers to the initial maximum height difference measured in step 1; For safety factors, the value ranges from 1.5 to 2.0; Step 4.2: Based on the removal depth of a single vertical cross-scan Cumulative removal depth with target Calculate the number of basic scan groups The number of scans per processing cycle is dynamically configured based on the large-scale removal or fine homogenization conditions characterized by the initial maximum height difference. ; Step 4.3: First, initialize the first round of planned scan count, surface roughness baseline value, degradation counter, historical best roughness, and convergence threshold, then... After the wheel machining is completed, the current cumulative removal depth and the current arithmetic mean roughness are obtained. Based on the change of the current arithmetic mean roughness relative to the previous round reference roughness, and the achievement of the current cumulative removal depth relative to the target cumulative removal depth, the degradation counter, historical best roughness and reference roughness are updated to establish an iterative execution and feedback control process. Step 4.4: Determine the termination condition based on the deterioration counter and the relative change rate of surface roughness. When quality deterioration occurs in two consecutive rounds and the current cumulative removal depth reaches or approaches the target cumulative removal depth, or when the relative change rate of surface roughness is less than the preset convergence threshold and the current cumulative removal depth reaches or approaches the target cumulative removal depth, or when the relative change rate of surface roughness in two consecutive rounds is less than the convergence threshold, terminate the processing and retain the historical best roughness state as the final result. Otherwise, increase the cumulative planned scan count and enter the next iteration.

3. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 2, characterized in that, In step 4.2, the number of basic scan groups for: ； In the formula: The cumulative removal depth of the target; d is the removal depth of a single vertical cross-scan. It is a rounding function; Number of scans per round according to The surface to be processed is divided into "large allowance removal condition" or "fine homogenization condition". When step 1 identifies the surface to be processed as being in the large allowance removal condition, Set to a larger value; when step 1 identifies the surface to be processed as being in a fine homogenization condition, Set to a smaller value.

4. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 2, characterized in that, In step 4.3, before officially entering the first round of processing, the state initialization for round 0 is performed first, and the number of planned scans for the first round is set. The initial arithmetic mean roughness measured in step 1 is... Set as the reference value for surface roughness in the previous round and initialize the degradation counter. Historical best roughness and convergence threshold The convergence threshold The value range is 3%-5%; In the Obtain the current cumulative removal depth after the wheel processing is completed. and the current arithmetic mean roughness and will Compared with the previous reference roughness as well as Cumulative removal depth with target Perform joint comparison; when and or At that time, update the deterioration counter to ;when and At the same time, the degradation counter remains unchanged, and the reference roughness is... Keep unchanged or press Update; when At that time, the deterioration counter will be reset to zero, and in Update historical best roughness At the same time Updated to .

5. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 2, characterized in that, In step 4.4, based on the deterioration counter To determine the protection against persistent degradation, when And the current cumulative removal depth meets the requirements. or If the processing is determined to have entered a stage of continuous quality degradation, processing should be terminated immediately, and the historical best surface roughness should be retained. The corresponding state is taken as the final result.

6. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 2, characterized in that, In step 4.4, the relative change rate of surface roughness Calculate using the following formula: ； In the formula: The surface roughness reference value from the previous round before entering this round of judgment; The current arithmetic mean roughness obtained in this round of testing; the convergence threshold. The value range is 3%-5%; when and When the processing reaches a convergence state, the processing is terminated; or when two consecutive rounds satisfy the condition... If the above termination conditions are not met, the cumulative planned scan count is updated. Then, it will proceed to the next round of iterative processing.

7. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 1, characterized in that, In step 3, pulse overlap rate Scan line overlap rate ,when At that time, we can obtain: ； In the formula: v is the laser repetition frequency; v is the galvanometer scanning speed. The diameter of the processing spot; L is the line spacing between two adjacent scan lines.

8. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 1, characterized in that, In step 3, the vertical cross-scanning strategy specifically includes: setting the area to be processed as a processing path containing at least two scanning levels, wherein the scanning direction of the i-th scanning path is perpendicular to the scanning direction of the (i+1)-th scanning path; within each scanning level, the scanning speed v of the galvanometer system and the repetition frequency of the laser are controlled collaboratively. This results in a higher overlap rate between adjacent pulse spots along the scanning direction. Satisfying 50%≤ ≤98%; simultaneously, the line spacing L between adjacent scan trajectories is set to ensure that the overlap rate of scan lines perpendicular to the scanning direction is ≤98%; Satisfying 50%≤ ≤98%; where the spot overlap rate overlap with scan line They are configured to be equal, or the absolute value of the difference between the two is ≤10%, in order to achieve isotropic energy deposition on the workpiece surface and uniform distribution of removal amount.

9. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 1, characterized in that, The laser removal strategy in step 1 includes a rapid peak-shaving mode for surfaces with large margins and a fine homogenization mode for surfaces with small margins. The rapid peak-shaving mode is used when the initial maximum height difference is greater than a preset threshold, and the fine homogenization mode is used when the initial maximum height difference is less than or equal to the preset threshold.

10. The ultrafast laser processing method for metal workpieces based on surface quality feedback according to claim 1, characterized in that, In step 2, the laser energy density is slightly higher than the material ablation threshold. The average output power of the laser is controlled to ensure that the single-pulse laser energy density on the defocused surface is... satisfy: ； In the formula: The single-pulse ablation threshold of the material; For safety factors, the value ranges from 1.05 to 1.35; laser average output power for: ； In the formula: For safety factor; The single-pulse ablation threshold of the material; The repetition frequency of the laser; Defocus amount The actual effective spot radius at the location; This is the defocusing amount.

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